runtime: initial windows/arm64 implementation files

This CL adds a few small files - defs, os, and rt0 - to start
on windows/arm64 support for the runtime.

It also copies sys_windows_arm.s to sys_windows_arm64.s,
with the addition of "#ifdef NOT_PORTED" around the entire file.
This is meant to make future CLs easier to review, since the
general pattern is to translate the 32-bit ARM assembly into
64-bit ARM assembly.

This CL is part of a stack adding windows/arm64
support (#36439), intended to land in the Go 1.17 cycle.

Change-Id: I922037eb3890e77bac48281ecaa8e489595675be
Reviewed-on: https://go-review.googlesource.com/c/go/+/288827
Trust: Russ Cox <rsc@golang.org>
Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com>

src/runtime/defs_windows_arm64.go

@@ -0,0 +1,83 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package runtime
+
+// NOTE(rsc): _CONTEXT_CONTROL is actually 0x400001 and should include PC, SP, and LR.
+// However, empirically, LR doesn't come along on Windows 10
+// unless you also set _CONTEXT_INTEGER (0x400002).
+// Without LR, we skip over the next-to-bottom function in profiles
+// when the bottom function is frameless.
+// So we set both here, to make a working _CONTEXT_CONTROL.
+const _CONTEXT_CONTROL = 0x400003
+
+type neon128 struct {
+	low  uint64
+	high int64
+}
+
+// See https://docs.microsoft.com/en-us/windows/win32/api/winnt/ns-winnt-arm64_nt_context
+type context struct {
+	contextflags uint32
+	cpsr         uint32
+	x            [31]uint64 // fp is x[29], lr is x[30]
+	xsp          uint64
+	pc           uint64
+	v            [32]neon128
+	fpcr         uint32
+	fpsr         uint32
+	bcr          [8]uint32
+	bvr          [8]uint64
+	wcr          [2]uint32
+	wvr          [2]uint64
+}
+
+func (c *context) ip() uintptr { return uintptr(c.pc) }
+func (c *context) sp() uintptr { return uintptr(c.xsp) }
+func (c *context) lr() uintptr { return uintptr(c.x[30]) }
+
+func (c *context) set_ip(x uintptr) { c.pc = uint64(x) }
+func (c *context) set_sp(x uintptr) { c.xsp = uint64(x) }
+func (c *context) set_lr(x uintptr) { c.x[30] = uint64(x) }
+
+func dumpregs(r *context) {
+	print("r0   ", hex(r.x[0]), "\n")
+	print("r1   ", hex(r.x[1]), "\n")
+	print("r2   ", hex(r.x[2]), "\n")
+	print("r3   ", hex(r.x[3]), "\n")
+	print("r4   ", hex(r.x[4]), "\n")
+	print("r5   ", hex(r.x[5]), "\n")
+	print("r6   ", hex(r.x[6]), "\n")
+	print("r7   ", hex(r.x[7]), "\n")
+	print("r8   ", hex(r.x[8]), "\n")
+	print("r9   ", hex(r.x[9]), "\n")
+	print("r10  ", hex(r.x[10]), "\n")
+	print("r11  ", hex(r.x[11]), "\n")
+	print("r12  ", hex(r.x[12]), "\n")
+	print("r13  ", hex(r.x[13]), "\n")
+	print("r14  ", hex(r.x[14]), "\n")
+	print("r15  ", hex(r.x[15]), "\n")
+	print("r16  ", hex(r.x[16]), "\n")
+	print("r17  ", hex(r.x[17]), "\n")
+	print("r18  ", hex(r.x[18]), "\n")
+	print("r19  ", hex(r.x[19]), "\n")
+	print("r20  ", hex(r.x[20]), "\n")
+	print("r21  ", hex(r.x[21]), "\n")
+	print("r22  ", hex(r.x[22]), "\n")
+	print("r23  ", hex(r.x[23]), "\n")
+	print("r24  ", hex(r.x[24]), "\n")
+	print("r25  ", hex(r.x[25]), "\n")
+	print("r26  ", hex(r.x[26]), "\n")
+	print("r27  ", hex(r.x[27]), "\n")
+	print("r28  ", hex(r.x[28]), "\n")
+	print("r29  ", hex(r.x[29]), "\n")
+	print("lr   ", hex(r.x[30]), "\n")
+	print("sp   ", hex(r.xsp), "\n")
+	print("pc   ", hex(r.pc), "\n")
+	print("cpsr ", hex(r.cpsr), "\n")
+}
+
+func stackcheck() {
+	// TODO: not implemented on ARM
+}

src/runtime/os_windows_arm64.go

@@ -0,0 +1,14 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package runtime
+
+import "unsafe"
+
+//go:nosplit
+func cputicks() int64 {
+	var counter int64
+	stdcall1(_QueryPerformanceCounter, uintptr(unsafe.Pointer(&counter)))
+	return counter
+}

src/runtime/rt0_windows_arm64.s

@@ -0,0 +1,12 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include "go_asm.h"
+#include "go_tls.h"
+#include "textflag.h"
+
+// This is the entry point for the program from the
+// kernel for an ordinary -buildmode=exe program.
+TEXT _rt0_arm64_windows(SB),NOSPLIT|NOFRAME,$0
+	B	·rt0_go(SB)